As an exposure apparatus used in a semiconductor manufacturing process, there have conventionally been known an apparatus called a stepper and an apparatus called a scanner. The stepper reduces a pattern image formed on a reticle and projects the pattern image onto a semiconductor wafer on a stage apparatus via a projection lens while moving step by step the wafer below the projection lens, thus sequentially exposing a plurality of portions on one wafer. The scanner relatively moves a wafer on a wafer stage and a reticle on a reticle stage with respect to a projection lens, emits slit-shaped exposure light during relative movement (scanning movement), and projects the reticle pattern onto the wafer. The stepper and scanner are considered to be the mainstream of exposure apparatuses in terms of the resolution and overlay accuracy.
One of the apparatus performance indices is the throughput, which represents the number of wafers processed per unit time. To realize a high throughput, high-speed movement is required for the wafer stage and reticle stage. A conventional reticle stage capable of high-speed driving with little heat generation is disclosed in Japanese Patent Laid-Open No 2000-106344.
In the conventional exposure apparatus, however, a current flowing through the driving coil of an electromagnet contains an offset current under the influence of a disturbance, even in the absence of any command information to the electromagnet. Even a small offset current causes a force error, failing to generate an accurate force.